EP0754841B1 - Process and device for purifying motor vehicle exhaust gases - Google Patents

Description

The invention relates to a device for exhaust gas purification Motor vehicles, with an adsorber, optional flaps Actuation of the adsorber with the exhaust gas flow during the Adsorptionsvorgangs and during the rinsing process, a downstream the adsorber located main catalyst, downstream of the Adsorber arranged sensor for determining the Gas composition, arranged upstream of the absorber additional sensor for determining the gas composition, and a control unit of which, depending on the signals of the Sensors, the flaps are controlled, such that the Exhaust gas stream aufschaltbar on the adsorber or by him can be switched off.

A starting point for further reducing the Pollutant emissions from being provided with a catalyst Motor vehicles provides the warm-up phase of the catalytic Systems, because starting from the cold state of the motor vehicle and thus the catalytic system of the motor vehicle unpurified raw exhaust gas is emitted. Because that catalytic system only from a certain light-off temperature, also called light-off temperature, an effective emission control can perform, the catalytic system is especially at Cold start of the vehicle engine, i. the motor vehicle driving internal combustion engine largely ineffective.

To remedy this situation, it was state of the art For example, it is known to preheat the catalyst from the outside, so that this as soon as possible his light-off reached. The light-off temperature is understood as meaning the one Temperature of the catalyst, in which this one not realized immaterial conversion rate, the for example, at least 30 to 50%.

As another approach, it was the prior art known to use adsorbers which are able To store exhaust gas components at low temperatures (to adsorb) and at higher temperatures again to deliver (to desorb). The adsorption capacity is greater, the lower the gas and adsorber temperature is. That means, that in the start-up and warm-up phase, when the catalytic System is still ineffective, from that the catalytic system upstream adsorber certain exhaust gas components adsorbed and only be released again when the catalytic System has reached its operating temperature. In this way The adsorber can be an ideal complement to the catalytic Represent system.

However, the adsorption capacity of the adsorbent first decreases with increasing temperature of the adsorber or with rising Exhaust gas temperature and then even the desorption of the Adsorbers before the subsequent catalytic system its Has reached light-off temperature. The non-adsorbed or even desorbed exhaust gas components then flow through without After-reaction the catalytic system. Since the adsorber only at comparatively low temperatures is effective, the Catalyst only at comparatively high temperatures, Thus, due to the system, there is an intermediate period, in which neither the adsorber, nor the catalyst is sufficient are effective, or even worse, the adsorber itself desorbed while the catalyst is not yet effective is.

A device according to the introductory part of Claim 1 is known from JP 07042542 A. The sensors can be used as hydrogen concentration or oxygen concentration sensors be executed, the adsorption process is terminated when the difference of the measured values of the two Sensors exceeds a predetermined value. After this Reaching the light-off temperature of the main catalyst is the Exhaust gas flow due to a temperature signal again through the Adsorber passed to rinse this and for the to reprocess the next cold start of the engine.

By the invention, the task is solved, a device of the type mentioned above for the emission control To create motor vehicles, with an optimal interaction between the adsorber and the catalytic system so takes place that in all operating phases of the Motor vehicle exhaust purification takes place.

According to the invention, the sensors are designed as lambda probes which have an effective at least in terms of the conversion of HC and O ₂ catalytic coating, wherein the respectively detected by the sensors exhaust stream is first passed over the coating and subsequently to the lambda probe, said during the adsorption process of the controller, the exhaust stream is not further passed through the adsorber when the gas composition detected by the downstream sensor downstream of the adsorber has HC contents, and during the purge from the controller, the exhaust gas flow from the adsorber is shut off when that from the downstream sensor determined gas composition downstream of the adsorber is equal to the determined by the additional sensor gas composition upstream of the adsorber (3).

In one embodiment of the invention can upstream of the Main catalyst, preferably also upstream of the adsorber, a starting catalyst may be provided.

By arranging the adsorber in a bypass and a controller by means of the exhaust valves, as well as by means of a close to the Motor output arranged and thus relatively fast heating starting catalyst is allowed that the catalytic system interacts with the adsorber so that the Starting catalyst has already reached its light-off temperature, while the adsorber still has high activity, but conversely, no rinsing takes place before, not even the further back in the exhaust stream located main catalyst its Has reached light-off temperature. It can be provided that the exhaust stream for purging or discharging the adsorber after Reaching the light-off temperature of the main catalyst in a row first the start catalyst, then the adsorber and then the Main catalyst flows through. Similarly, after reaching the light-off temperature of the main catalyst of the exhaust gas flow to Rinsing or discharging the adsorber in sequence first Flow starting catalyst, then divided into two streams of which one of the two partial streams through the adsorber flows and both partial flows behind the adsorber again then merge together through the main catalyst stream.

This offers the advantage that the starting catalyst as close as possible to be placed on the motor output, thereby heats up quickly and thereby cools the exhaust stream, which subsequently flows through the adsorber arranged in the bypass. As a result, on the one hand, the starting catalyst is heated quickly and thus quickly effective, while on the other hand, the adsorber so is kept cool as long as possible and so too maintains its effectiveness for a relatively long time.

After sufficient purging of the adsorber, the exhaust gas flow, if necessary from the starting catalyst, again directly into the Passed main catalyst, causing the adsorber after rinsing or after desorption, from impurities as well thermal load is saved by the exhaust gas flow. Also So can the flow conditions for the set steady state or continuous operation optimally. After sufficient rinsing of the adsorber, the Exhaust gas flow for continuous operation directly from the engine through the Main catalyst are passed. For this purpose, the Starting catalyst be provided with a switchable bypass, further comprising an exhaust flap for applying the Starting catalyst or the bypass with the exhaust stream is provided. This has the advantage that the Starting catalyst on the one hand only for relatively short-term Operation must be designed, and on the other hand on the Starting catalyst such flow conditions set can be that this heats up very quickly, without thereby adversely affecting the continuous operation.

This can be realized, for example, that the branching off before the start catalyst bypass line on the input side with the input or output side with the Output of the adsorber is connected, the output side Part of the bypass line opens into those pipeline part, which the output of the starting catalyst with the input of the Main catalyst connects, and in addition behind the Starting catalyst of that pipe part, which the Output of starting catalyst with the input of the Main catalytic converter connects, a connecting line branches, which with the bypass line on the input side based on the Adsorber is connected.

It is also possible that the bypass line before the Starting catalyst branches off from that pipeline part, which the output of the motor with the input of the Starting catalyst connects, the bypass line on the input side with the input or output side with the Output of the adsorber is connected, the output side Part of the bypass line again in those pipeline part which connects the output of the motor with the input of the motor Start catalyst connects.

It can be advantageous in that pipeline part, which connecting the engine to the inlet of the starting catalyst, behind the branch point for the bypass line to one be provided opening and closing exhaust flap. there even the starting catalyst and the main catalyst can be added a single component are summarized, so that this together form a single catalyst, which is constructive is advantageous to realize. It can be a little disadvantageous at most affect that the adsorber closer to the engine is arranged as the starting catalyst and thus earlier is heated while the starting catalyst is slower is heated.

Figuren 1 bis 4 vier Untervarianten eines ersten Ausführungsbeispiels in schematischer Darstellung;

Figur 5 ein zweites Ausführungsbeispiel in schematischer Darstellung;

Figur 6 ein drittes Ausführungsbeispiel in schematischer Darstellung;

Figur 7 ein viertes Asuführungsbeispiel in schematischer Darstellung;

Figur 8 ein Diagramm, welches die Adsorberspeichervolumenrate in Abhängigkeit von der Temperatur bzw. Zeit zeigt;

Figur 9 ein Diagramm, welches die Startkatalysator-Umwandlungsrate in Abhängigkeit von der Temperatur bzw. Zeit zeigt; und

Figur 10 ein Diagramm, welches die adsorbierte bzw.

konvertierte Abgasvolumenrate über der Temperatur bzw. Zeit zeigt.The invention will be described below
of preferred embodiments with reference to the drawings. In the drawing show:

Figures 1 to 4 four sub-variants of a first embodiment in a schematic representation;

Figure 5 shows a second embodiment in a schematic representation;

Figure 6 shows a third embodiment in a schematic representation;

Figure 7 is a fourth Asuführungsbeispiel in a schematic representation;

Figure 8 is a graph showing the adsorber storage volume rate versus temperature and time, respectively;

Figure 9 is a graph showing the starting catalyst conversion rate versus temperature and time, respectively; and

FIG. 10 is a diagram which shows the adsorbed or

converted exhaust gas volume rate over the temperature or time shows.

As can be seen from Figure 1, are a motor 1, a Starting catalyst 2, an adsorber 3 and a main catalyst. 4 connected by means of a piping system. there a first pipe part 5 extends between the Output of the engine 1 and the input of the starting catalyst 2, a second pipe part 6 extends between the Output of starting catalyst 2 and the input of the Main catalyst 4, and a third pipe part 7 leads away from the main catalyst 4, for example, to an exhaust out. The adsorber 3 is arranged in a bypass line 8, which on the input side of the aforementioned pipe section 6 based on the adsorber 3 opens, and the output side based on the adsorber 3 back into the pipe part. 6 opens. In the embodiment of Figure 1 are in the Bypass line before and behind the adsorber 3 each one to opening and closing exhaust flap 9 or 10 provided, and in the pipe part 6, which is located between the Start catalyst 2 and the main catalyst 4 extends is on the place which lies between the point of discharge the bypass line 8 and the junction of the bypass line. 8 is another one to open and close Exhaust flap 11 is arranged.

Immediately upstream of the main catalytic converter 4 is a sensor 18 arranged, the gas composition of the exhaust stream detected at least in terms of the exhaust gas component HC. Depending on Position of the exhaust valves 9, 10 and 11, the sensor 18 with the guided through the adsorber 3 exhaust stream, which from the Starting catalyst 2 exiting exhaust stream or a mixture charged therefrom.

Behind the engine 1, a lambda probe 19 is also present, for a lambda control for the mixture preparation of the Engine 1 is provided. The lambda probe 19 is usually arranged downstream of the starting catalyst 2; she can, however be arranged upstream of the starting catalyst 2, if it allow the thermal conditions.

To control the exhaust valves 9, 10 and 11 is a control unit 20 provided that the signals of the sensor 18 and the Lambda probe 19 receives and determines which of the Exhaust flaps 9, 10 or 11 to open or close.

The embodiments shown in FIGS. 2 to 4 represent subvariants of the embodiment of Figure 1 are according to the embodiment of Figure 2 only the Exhaust flaps 10 and 11 provided, according to Figure 3 only the Exhaust flaps 9 and 11 provided, and as a minimum solution according to the embodiment shown in Figure 4 only the Exhaust flap 11 is provided.

Another embodiment is shown in FIG. 5, wherein the same Components designated by the same reference numerals as in Figure 1 are, the lambda probe 19 in Fig. 5 but not shown is .. In the embodiment of Figure 5 branches the Bypass 8 but not as shown in Figure 1 of the itself between the start catalyst 2 and the main catalyst 4 extending pipe part 6, but already empties between the output of the motor and the input of the motor Starting catalyst 2 extending pipe part 5 and before the start catalyst 2 again in this one. Therefore, too not as shown in Figure 1 to be opened and closed Exhaust flap in the pipe part 6, but in the Pipe part 5 between the Ausmündungs- and Junction of the bypass line 8 based on the Pipe part 5 is arranged. This exhaust flap is in the Drawing designated by the reference numeral 12. Analogous to the Exemplary embodiments according to FIGS. 2 to 4 can also be used at the embodiment of Figure 5, the exhaust valves 9 and 10th optionally omitted or provided.

Another embodiment is shown in FIG. 6, where as well in the figures 1 and 5 the same elements with the same Reference signs are designated, the lambda probe 19, however, not is drawn. Referring to the embodiments of FIG 5 is in the embodiment of Figure 6 additionally a Connecting line 13 is provided, which the pipe part. 5 the output side based on the adsorber with the bypass line. 8 connects, and there are 2 more exhaust valves 14 and 15 provided, of which an exhaust flap 14 immediately before the Starting catalyst behind the branch point of Branch line 13 is disposed in the pipe part 5, and the other exhaust valve 15 in the bypass line. 8 the output side based on the adsorber 3 behind the Junction of the branch line 13 in the bypass line 8 is arranged. The bypass line 8 opens altogether from the Pipe part 5 from and into the pipe part 6 a.

A final embodiment is shown in Figure 7, wherein the same elements as in Figures 1, 5 and 6 with the same reference numerals are designated, the lambda probe 19th but not shown. Compared with the Embodiment of Figure 6 is in the Embodiment of Figure 7 of the adsorber, however, in the Bypass line between a connecting line 16, which from the pipe part 6 opens behind the start catalyst 2 and input side based on the adsorber 3 in the Bypass line 8 opens, and the output side of the adsorber again in the pipe part 6 opening part of the Bypass 8 arranged. In addition, an exhaust flap 17 arranged in the bypass line 8 in front of that point at which the connecting line 16 in the bypass line. 8 opens.

In the embodiments according to FIGS. 6 and 7, instead of of the compared with Fig. 5 additional branch of Bypass line 8 and the added exhaust valves 14, 15, 17 also a special training of the starting catalyst. 2 can be used, as for example from DE-A-39 30 380 (= JP-A-3100313) is known. This start catalyst 2 has a central channel provided with an exhaust flap, which is surrounded by a bypass annular gap. When closed Exhaust flap, the exhaust stream flows through the annular gap, whereas with open exhaust flap almost exclusively the Central channel is flowed through, since its flow resistance is significantly smaller than that of the annular gap.

The adsorption characteristics of the adsorber or the Conversion characteristics of the starting catalyst show the Diagrams according to FIGS. 8 to 10. As FIG. 8 shows, FIG the adsorber on start of operation on a high storage rate, i.e. He can per unit of time a large volume of pollutants to save. As the time progresses, the fills up Adsorber and also assumes a higher temperature, which the volume that can be stored per unit of time decreases.

In contrast, the starting catalyst conversion rate is too high Start of operation low and increases only after a certain Dead time or from a certain temperature on relatively steep.

The design of the starting catalyst and the adsorber is so chosen that the intersection of both curves is such that he as high as possible between 0 and 100%, which means that then it is ensured that the adsorber is still a high Adsorberspeichervolumenrate ensured while that of the Starting catalyst also converted exhaust gas volume already is relatively high.

The operation of the embodiments of Figures 1 to 7 is as follows:

After starting the engine is first the exhaust valve 11th closed in the embodiment of Figure 1, thereby the exhaust gas flow from the engine through the pipe part 5 through the start catalyst 2 in the bypass line 8 through the adsorber 3 and back into the pipeline part 6 and finally through the main catalyst 4 and by means of the Pipe part 7 flows into the exhaust. Here are the Exhaust flaps 9 and 10 open. After the starting catalyst his Has reached light-off temperature, or after the adsorber. 3 only a negligible effect due to the Heating or due to the fully utilized storage volume has, the exhaust valves 9 and 10 are closed and the Exhaust flap 11 is opened, after which the main catalyst. 4 Opportunity obtains up to its light-off temperature heat. Thereafter, the exhaust valve 11 is closed again and the exhaust valves 9 and 10 are opened again, whereby the Adsorber 3 is purged by hot exhaust gas through it is passed, which for the desorption of the beginning in the Adsorber adsorbed pollutants leads. These will be then passed through the main catalyst 4, where the exhaust gas flow, which additionally with the desorbed exhaust components enriched in the main catalyst 4 are converted can.

After flushing, wherein the time in which the flushing or desorption is completed by the Exhaust gas sensors 18, 19 is detected, the exhaust valves 9 and 10 closed again, whereby the adsorber 3 completely isolated from the exhaust stream; and after a later shutdown and cooling the engine and the starting catalyst 2 and the Main catalyst 4 is ready for a new operation.

As a minimal solution, it is also possible, as in the Embodiment of Figure 4, only a single exhaust flap To provide 11, which already be achieved in this way can that at the beginning of the operation of the full exhaust stream for the purpose Adsorption is passed through the adsorber 3, as well as later again completely passed through the adsorber 3 for flushing becomes. However, it always flows even when the exhaust flap 11 is open a small, possibly undesirable partial exhaust stream through the adsorber 3. By constructive design of the bypass exhaust pipe must therefore be prevented before the adsorber the adsorber in this phase by the partial exhaust gas on is heated up and begins here already with the desorption. On the other hand, it must be prevented that after successful Adsorption and desorption in normal operation even through the adsorber flowing partial exhaust stream is cooled too much and the adsorber adsorbed. This would mean that in next cold start only a part of the whole Adsorbervolumens could be used. Remedy can be like here according to Figures 2 and 3, each with only one exhaust flap 9 or 10 are created.

In the embodiment of Figure 5 are at Start of operation, the exhaust valves 9 and 10 open and the Exhaust flap 12 is closed, whereby the entire exhaust gas flow from the engine 1 via the pipe part 5 by means of Bypass line 8 through the adsorber 3 back into the Pipe part 5 and then through the start catalyst 2 and by means of the pipe part 6 through the main catalyst. 4 and led by means of the pipe part 7 in the exhaust and adsorption of exhaust gas volume in the adsorber 3 can take place. After the starting catalyst his Has reached light-off, the exhaust valve 12 opened and the exhaust valves 9 and 10 are closed, whereby the exhaust gas flow directly from the engine 1 by means of Pipe part 5 through the start catalyst 2 and means of the pipe part 6 through the main catalyst 4 and of There by means of the pipe part 7 to the exhaust is transported. After the main catalyst 4 its Has reached light-off, the exhaust valve 12 is again closed and the exhaust valves 9 and 10 are again opened, whereby the adsorber 3 can be rinsed. The way Desorbed pollutants can then both in the Starting catalyst 2, as well as in the main catalyst. 4 afterreact. Finally, the exhaust valve 12 is again opened and the exhaust valves 9 and 10 are again closed, whereby the exhaust gas flow from the engine through the Pipe part 5 directly into the starting catalyst 2 and further by means of the pipe part 6 in the main catalyst 4 is headed.

In the embodiment shown in Figure 6 are at Start of operation, first the exhaust flaps 12 and 15 closed, and the exhaust valves 9, 10 and 14 are opened, whereby the Exhaust gas stream first through the adsorber 3, then through the Starting catalyst 2 and finally through the main catalyst. 4 flows. After the start catalyst 2 its light-off temperature has reached, the exhaust valve 12 is opened and the Exhaust flaps 9 and 10 are closed, whereby the First, exhaust gas flow only from the engine directly through the Starting catalyst 2 and then through the main catalyst. 4 flows. After reaching the light - off temperature of the Main catalytic converter 4, the exhaust valve 12 is closed and the Exhaust flaps 9 and 10 are opened, whereby the from the Adsorber desorbed exhaust components both in the Starting catalyst, as well as converted in the main catalyst can be. Optionally, those desorbed Exhaust gas components also converted only in the main catalyst be closed by the exhaust flap 14 and the Exhaust flap 15 is opened. After the adsorber sufficient finally, the exhaust flaps 9, 10, 14 closed and the exhaust flaps 12 and 14 are opened, whereby the exhaust gas flow from the engine 1 via the Pipe part 5 through the connecting line 13 on the bypass line 8 and the pipe part 6 directly into the Main catalyst 4 and from this via the pipe part 7th out into the exhaust. Optionally, you can also the flaps 8,9 and 14 closed and the flaps 12 and 15 are opened, which then the exhaust stream directly from Engine 1 through the main catalyst 4 and from there through the Exhaust can flow into the open air.

A final embodiment is shown in Figure 7, wherein At the beginning of operation, first the exhaust valves 11 and 17th closed and exhaust flaps 14, 9 and 10 are open, whereby the exhaust gas flow from the engine 1 through the Pipe part 5 and subsequently through the start catalyst. 2 by means of the connecting line 16 and further by means of Bypass line 8 through the adsorber 3 back into the Pipe part 6 and flows through the main catalyst 4. After reaching the light-off temperature by the Starting catalyst 2 or after the adsorber 3 is no longer his has maximum adsorption capacity, the exhaust valves 9 and 10 in addition to the exhaust valve 17 is closed and the Exhaust flaps 14 and 11 are opened, whereby the exhaust gas flow from the engine 1 directly through the starting catalyst 2 and then can be passed through the main catalyst 4. After, too the main catalyst 4 has reached its light-off temperature, the exhaust valve 11 is closed again and the exhaust valves 9 and 10 are opened, whereby the exhaust gas flow through first the starting catalyst 2 through the connecting line 16 by Adsorber 3 can flow into the main catalyst 4 and the Adsorber 3 is flushed or discharged. After complete Discharge of the adsorber 3, the exhaust valves 9 and 10th closed again and the exhaust valve 11 is opened and the Exhaust gas flow may be from the engine directly through the startup catalyst 2 and then flow through the main catalyst 4. Then can optionally, the exhaust valve 14 are closed, and the Exhaust flap 17 are opened, the previously already opened exhaust flap 11 in its open state and the already closed exhaust valves 9 and 10 in their closed state remain. This allows the exhaust gas flow of the engine 1 by means of the bypass line 8 through the Connecting line 16 and by means of the pipe part 6th flow directly through the main catalyst 4, whereby the Starting catalyst during long-distance operation of the vehicle is completely turned off and spared in this way becomes.

The control of the exhaust valves 10, 11 will now be based on the in Fig. 2 illustrated embodiment will be explained. At a cold start of the engine, the Exhaust flap 11 is closed and the exhaust valve 10 is open, so that the exhaust gas stream is passed completely through the adsorber 3 becomes. The sensor 18 detects in this switching state of Exhaust flaps 10, 11 the exhaust gas flow on the output side of the adsorber Third

Experiments have shown that the point at which desorption begins in the adsorber 3 is not dependent solely on the temperature of the adsorber 3, but additionally on the HC concentration of the exhaust gas stream entering the adsorber 3. Therefore, with a procedure based on a temperature detection, the time at which the adsorber 3 is no longer receptive can only be approximately determined. A much more accurate determination of this point in time is possible if the sensor 18 determines the gas composition, in particular the HC content, in the exhaust gas flow downstream of the adsorber 3. For this purpose, a lambda probe is used according to the invention, which is surrounded by a catalytically active layer. The catalytic layer is chosen so that preferably takes place a reaction of HC and O ₂ . As long as no HC is present in the exhaust gas stream, ie the adsorber 3 is able to absorb the HC present in the exhaust gas stream, the O _{2 present} in the exhaust gas stream can pass the catalytic layer and reach the actual lambda probe and generate a corresponding signal here. Is contained in the exhaust stream downstream of the adsorber 3 HC, ie the adsorber 3 is saturated, so that HC breaks through the adsorber 3, react in the catalytic layer HC and O ₂ , so that no further O _{2 can get} to the actual lambda probe and again generates a corresponding signal. In order to be able to receive a signal from the lambda probe 18 even during a cold start, it must be heated in a known manner, including the catalytic layer.

Detects the controller 20 on the supplied from the sensor 18 Signal that the limit value HC is contained in the exhaust stream, i. the saturation limit of the adsorber 3 is reached, so closes the controller 20, the exhaust valve 10 and opens at the same time the exhaust flap 11. With the above-described Procedures, it is possible at a cold start of the engine 1 by controlling the exhaust valves 10, 11 the exhaust gas flow exactly to conduct over the adsorber 3 as long as this able is to record HC. Thus, on the one hand the Storage capacity of the adsorber independent of the Environmental conditions exploited best possible, on the other hand is ensure that the adsorber 3 no longer than makes sense with the exhaust stream is applied and to a as early as possible the exhaust gas flow directly to the Main catalyst 4 can be routed so that this fast reached its activation temperature and for a effective exhaust gas purification ensures.

Also, the rinsing of the adsorber 3 after reaching the Light-off temperature is controlled by means of the sensor 18. In addition, the signal of the lambda probe 19 is used, which is arranged upstream of the adsorber 3. Because the Lambda probe 19, if it is behind the start catalyst 2 is arranged, the gas composition immediately before Adsorber 3 detected, it is now possible, the signal of the Compare sensors 18 with the signal of the lambda probe 19. This comparison is particularly easy to perform when the Sensor 18 and the lambda probe 19 are identical parts. In In this case, the rinsing of the adsorber 3 by opening the Exhaust flap 10 and closing the exhaust valve 11 so long until the signals of the sensor 18 and the lambda probe 19 are the same. At this time, the exhaust gas flow passes through the adsorber 3, without a change in the composition of the exhaust stream takes place in the adsorber 3 and the adsorber 3 thus completely is desorbed.

If the sensor 18 and the lambda probe 19 are not identical or the lambda probe before the start catalyst 2 is arranged, must be before flushing the adsorber 3, i. yet with the exhaust flap 10 closed and the exhaust flap 11 open, the difference of the signals of the sensor 18 and the lambda probe 19 are formed and stored. The rinsing of the adsorber 3 is then carried out until the difference of Signals again reached the previously stored value.

When a warm or hot start of the engine 1 is based on a characteristic temperature of the engine 1, this can for example, be the cooling water or oil temperature, decided whether at the start of the engine 1, the adsorber 3 is switched on. If the adsorber 3 is switched on or was he does not in a previous phase of operation of the engine 1 completely discharged, so there is a purging of the adsorber. 3 after the procedure described above, as soon as it is ensured that the main catalyst 4 his Activation temperature has reached.

Even if in all embodiments, a starting catalyst. 2 is provided upstream of the adsorber 3, so it is on it to point out that an operation of the entire system in the same Way without the start catalyst 2 is possible. At this Arrangement also takes place an effective reduction of HC components in the exhaust gas flow during the time during which the Exhaust gas flow through the adsorber 3 is passed. Because after the Turning off the adsorber 3 of the main catalyst 4 its Operating temperature has not reached, are now downstream of the main catalyst 4 to detect increased HC levels, as in Comparison with the illustrated embodiments now no Implementation in starting catalyst 2 more takes place. There on the other hand by the service life of the engine 1 during the Period of time during which the exhaust gas flow through the adsorber 3rd is led, heats up significantly, reaches the Main catalyst 4 significantly faster Light-off temperature, so that the total emissions during the Starting process even without the start catalyst 2 clearly are reduced.

Finally, it should be noted that when driving the Exhaust flaps 10, 11 it especially when purging the adsorber third not absolutely necessary, the entire exhaust flow through to direct the adsorber 3. Rather, it is also possible only a partial flow of the exhaust gas flow through the adsorber third through pass.

The above with reference to the embodiment of FIG. 2 described control of the exhaust valves 9, 10 and 11 is in the same way to control the exhaust valves 9, 10, 11, 12, 13, 14, 15 and 17 in the embodiments of FIGS. 1 and 3 applied to 7, as far as these are used to the Adsorber 3 to act on the exhaust stream.

Claims (4)

1. A device for exhaust purification in a motor vehicle having an absorber (3), valves (9, 10, 11) for optional exposure of said absorber (3) to an exhaust stream during absorption event and scavenging event, a main catalyst (4) arranged downstream from said absorber (3), a sensor (18) arranged downstream from said absorber (3) to determine a gas composition, an additional sensor (19) arranged upstream from said absorber (3) to determine the gas composition, and a control device (20) controlling said valves (9, 10, 11) depending on signals from said sensors (18, 19) such that the exhaust stream is conducted through said absorber (3) and disconnected there from respectively, wherein said sensors (18, 19) are formed as Lambda probes having a catalytic coating at least for a conversion of HC and O₂, and wherein said respective exhaust stream to which said sensors (18, 19) are exposed is conducted first over said catalytic coating and then to said lambda probe, said exhaust stream being no longer conducted through said absorber (3) by said control device (20) during the absorption event when the gas composition downstream from said absorber (3) as determined by said sensor (18) contains HC, and the exhaust stream is disabled by said control device (20) during the scavenging event when the gas composition downstream from said absorber (3) as determined by said sensor (18) is the same as the gas composition upstream from said absorber (3) as determined by said additional sensor (19).
2. A device according to claim 1, wherein a starting catalyst (2) is arranged upstream from said main catalyst (4).
3. A device according to claim 2, wherein said starting catalyst (2) is arranged upstream from said absorber (3).
4. A device according to claim 2, wherein said starting catalyst (2) has a bypass which can be connected in, and further wherein an exhaust valve (14, 15, 17) is provided to expose one of the starting catalyst (2) and the bypass to the exhaust stream.

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